(1) Field of the Invention:
The present invention relates to a process for joining ceramic members to metallic members through fitting. More particularly, the invention relates to a process for fitting and joining ceramic members to metallic members through press fitting, shrinkage fitting, expansion fitting, brazing or a combination thereof. Further, the present invention relates to composite bodies of ceramic members and metallic members produced by the above production process, for instance, the ceramic-metal composite bodies being rotary shafts for turbocharger rotors or gas turbine rotors.
The invention also relates to a joining apparatus used for effecting the above-mentioned process.
(2) Related Art Statement:
Recently, ceramic members have been used, for example, as turbine wheels in turbochargers and the like because of their excellent heat resistance, and rotary shafts of metallic members have been used as shafts for the ceramic members. The turbine wheel of a ceramic member is joined to the rotary shaft of a metallic member, for instance, by providing a recess at one end portion of the rotary shaft of the metallic member in an axial direction thereof, and fitting and joining a projection formed on the center portion of a back face of the turbine wheel of the ceramic member to the recess through shrinkage fitting, brazing or the like.
In such a joining structure, air is compressed in a space remaining in the recess after the joining and high pressure air is trapped therein. Therefore, press fitting, shrinkage fitting and the like have a drawback in that when a temperature rises at the joint portion, the projection slips off from the recess due to expansion of the trapped air. On the other hand, the brazing has a drawback in that the trapped air enters a joining interface between a brazing material and the ceramic member or between the brazing material and the metallic member so that a bonding area becomes smaller, alignment between the members to be joined together is deteriorated, or the fitting becomes insufficient, thereby resulting in poor joining.
As techniques for eliminating the abovementioned drawbacks, there have been proposed a joining structure in which a single air escape hole is provided passing from near a bottom face of a space inside a recess formed in a rotary shaft of a metallic member to a bottom end of the outer periphery of the recessed portion of the rotary shaft or near this bottom end (Japanese utility model registration application Laid-open No. 59-8,730 and Japanese patent application No. 60-77,180) and a joining structure in which a plurality of radial air escape holes are formed at an equal interval in a circumferential direction communicating with a space remaining at a deep portion of a recess in a rotary shaft of a metallic member (Japanese utility model registration application Laid-open No. 60-45,833).
However, the above two kinds of joining structures have the following problems.
That is, the joining structures described in Japanese utility model registration application Laid-open No. 59-8,730 and Japanese patent application Laid-open No. 60-77,180 have problems in that the shaft is vibrated during high speed rotation of the composite body. Further the rotary shaft of the composite body rotates under swing in an extreme case due to an unbalanced mass of the ceramic-metal composite body around a rotary shaft, because of a single air escape hole, as well as due to an unbalanced mass of the ceramic-metal composite body around the rotary shaft because of a bearing-lubricating lubricant which enters the space left in the recess through the air escape hole during a tie-up of rotation or a low speed rotation of the rotary shaft of the composite body and remains in the recess.
On the other hand, the joining structure of Japanese utility model registration application Laid-open No. 60-45,833 has a problem in that while the above-mentioned unbalanced mass of the composite body around the rotary shaft is to be eliminated by the provision of the air escape holes at the equal interval in the circumferential direction, the strength of the metallic rotary shaft and the joining strength decrease, because a plurality of the air escape holes are provided near the bottom of the recess in the rotary shaft of the metallic member.